basalt

Everyday

1. A hard, dark grey or black rock made when hot lava from a volcano cools quickly. tree →
2. (adjective use) Made of this rock: basalt columns. tree →

In the lessons

In science lessons on rocks, basalt is a classic igneous rock; much of the ocean floor is basalt. Famous basalt places include the Giant's Causeway in Northern Ireland with its six-sided columns. Phrases: basalt rock, basalt columns, basalt lava.

Examples

• Basalt forms when lava cools quickly. tree →
• The Giant's Causeway is made of thousands of basalt columns. tree →
• Basalt is dark and very hard. tree →
• Most of the ocean floor is made of basalt. tree →
• We sorted the rocks: granite, chalk and basalt. tree →
• Many columns have six sides, like hexagons. tree →

Note

Uncountable. Say BAS-awlt or buh-SAWLT. Basalt is igneous (made from melted rock), unlike chalk or sandstone, which are sedimentary. Basalt has tiny crystals because it cooled fast; granite has big crystals because it cooled slowly.